In communication technology, so called mixers are a frequently used circuit, which, as the name implies, mix a first and a second input signal, which are usually at respective first and second frequencies, and produce an output signal at a third frequency.
In a transceiver in a communications system, a mixer will usually be utilized in order to mix an intermediate frequency (IF) into a radio frequency (RF), or vice versa, mixing RF to IF.
A balun (“balanced-unbalanced”) is a component that converts a balanced signal into an unbalanced signal or vice versa, and which may be used together with certain kinds of mixers in which it is desired to convert an unbalanced input signal into a balanced one (or vice versa). A balun can be active or passive.
In a mixer, as has been explained above, two input signals are used, which means that with respect to the notion of balanced and unbalanced input signals, a number of cases can be discerned: If one of the input signals is unbalanced, that signal should be connected to the mixer via a balun, to convert it into a balanced signal. If both of the input signals are unbalanced, both of them need to be connected to the mixer via respective baluns, in order to convert the unbalanced input signals into balanced signals.